The prior art optical control is described in U.S. Pat. No. 4,859,965, issued Aug. 22, 1989. The prior art optical control includes a light source for emitting light at a wavelength in the region of 0.5 micrometers to 1 micrometer, control means coupled to said light source for controlling the intensity of the light emitted from said source, a fixed resistance, a GaAs multi-finger FET having parallel connected sources and parallel connected drains and parallel connected gate fingers, circuit means for connecting the sources and drains of said FET in series circuit with said fixed resistance across a source of positive dc voltage, optic fiber means optically coupled from said light source on the surface of said FET between the sources and drains of the FET and covering substantially all of the gate fingers of the FET, gate biasing means coupled to the gates of said FET for biasing said FET to a point near pinch-off to maximize the light sensitivity of the FET, dc amplifier means having an input coupled to a circuit junction of said fixed resistance and said FET and having an output, a GaAs MMIC distributed amplifier having a dc bias control coupled to the output of the dc amplifier means, whereby changes in the intensity of light from said light source change the voltage drop across said FET and the input applied to said dc amplifier means to thereby change the gains of said MMIC distributed amplifier.
One problem with the prior art optical control is that it is not suitable for controlling a microwave variable attenuator.
A related publication is by Paolella, A., Madjar, A., Herozfeld, P., Sturzebecher, D., entitled "Optically Controlled GaAs MMIC Switch using a MESFET as an Optical Detector", 1990 IEEE MTT-S International Microwave Symposium Digest, Volume II.
A related patent application is Ser. No. 07/604,081, filed Oct. 15, 1990, entitled "Optical Control of a Microwave Switch, of inventors, Sturzebecher, D., and Paolella, A.